1. Field of the Invention
This invention relates to finely divided particles of ammonium polyphosphate (APP) having a II type crystalline structure, the particle diameter of 80% by weight or more of the particles being 10 .mu.m or less, and the surface of the crystals being plain, and a process for producing the particles.
More particularly, the present invention relates to finely divided particles of APP which, when added or impregnated into the inside of polyolefin resins, molded products or fibers, afford products having a small reduction in the mechanical characteristics of polyolefins, molded products, fibers or the like, a reduced particle diameter and an increased specific surface area, and nevertheless having bleed resistance and flame retardancy similar to those of conventional products, and a process for producing the particles.
2. Description of the Related Art
It has been well known that APP is obtained by heat-condensing a mixture consisting of a phosphate-containing substance and an ammoniating-condensing agent. However, when conventional APP is added or impregnated into polyolefin resins, molded products, fibers or the like, in order to impart flame retardancy, the following disadvantageous problems are raised:
1. Unevenness of flame retardancy and reduction in the mechanical strengths, due to large particle diameter; PA1 2. reduction in the bleed resistance due to I type crystalline structure; PA1 3. reduction in the bleed resistance due to straining of the crystalline surface of APP, brought about by excess mechanical grinding; PA1 4. reduction in the bleed resistance due to insufficient viscosity of a suspension solution of 5% APP in hot water; etc. PA1 (1) Finely divided particles of synthesized ammonium polyphosphate (hereinafter abbreviated to APP) having a II type crystalline structure, 80% by weight or more of said particles having a particle diameter of 10 .mu.m or less. PA1 (2) Finely divided particles of APP according to item (1), wherein a 5% aqueous solution of said particles obtained by dissolving them in hot water at 80.degree. C. has a viscosity of 500 centiposes or more. PA1 (3) In the process for producing finely divided particles of APP by reacting ammonium phosphate with phosphorous anhydride, each in an equimolar quantity, in an ammonia gas atmosphere and at an elevated temperature, PA1 (4) A process for producing finely divided particles of APP according to item (3), wherein said ammonia-generating compound is a substance generating ammonia gas by heating urea, ammonium carbonate or ammonium carbamate, mixtures of the foregoing or aqueous solutions of the foregoing. PA1 (5) In the process for producing finely divided particles of ammonium polyphosphate by reacting ammonium phosphate with phosphorous anhydride, each in a nearly equimolar quantity, in an ammonia gas atmosphere and at an elevated temperature, PA1 (6) A production process according to item (5), wherein in said first reaction step of feeding no ammonia gas in nitrogen gas atmosphere, the reaction temperature is kept at 250.degree. to 320.degree. C. for 10 minutes or longer. PA1 (7) A production process according to item (5), wherein in the second step of instantaneously feeding ammonia or an ammoniating agent in 90% or less of the stoichiometric quantity, the time necessary for the feeding is made 5 to 30 minutes. PA1 (8) A production process according to item (5), wherein in the third reaction step of slowly adding ammonia gas and aging therewith, an atmospheric temperature of 240.degree. C. or higher is applied for 30 minutes or longer.
For example, according to Japanese patent publication No. Sho 53-11280, particles of APP having particle diameters as large as 63 .mu.m or less (average particle diameter: 15 .mu.m) occupy 94% by weight of the total particles; thus, when the particles are mechanically ground in order to finely grind them, the crystalline surface is strained to thereby raise the disadvantages described above in items 1 and 3. Further, according to Japanese patent publication Nos. Sho 53-15478 and Sho 49-30356, the resulting APPs have I type crystalline structure.
The object of the present invention is to provide finely divided particles of APP having solved the above-mentioned disadvantageous problems and a process for producing the same.